Lithographic printing techniques including offset lithography employ an image plate which is treated in such a way as to have hydrophilic areas which are receptive to water, but not ink, and hydrophobic areas which are receptive to ink, but exclude water. The image plate is contacted with a dampening system that applies an aqueous fountain solution to the hydrophilic portions of the plate and is contacted with an ink fountain which applies ink to the hydrophobic portions of the plate. The image plate then comes into contact with, and transfers the image to, a rubber blanket which in turn is brought into contact with a paper substrate, where the image is laid down to produce a printed sheet. The printing cycle is repeated continuously and at high speed.
As is well recognized in the art, print quality commonly deteriorates (e.g., blurring occurs at the edges of the printed and non-printed areas), with increased numbers of prints made since the last cleaning. This may be caused by accumulation of lint, dust, small pieces of paper, and the like on image plate or rubber blanket during the printing process. When this occurs, the press must be stopped to clean ink from the rubber blanket and/or other ink bearing parts of the press such as the rollers, ink train or the image plate. Most commonly, the rubber blanket becomes fouled and must be cleaned. This may be accomplished manually by rotating the printing press to locate the top of the rubber blanket and then removing all ink and foreign substances from the blanket, one section at a time, with a lint-free cloth saturated with a cleaning composition. After the rubber blanket is clean and dry, printing may be resumed. Thus, for an efficient printing operation it is important to be able to quickly and efficiently remove the ink and resume printing on the cleaned surfaces.
Until recently, the preferred cleaning fluids were solvents which are volatile organic compounds, such as mineral spirits, trichloroethylene, toluene, xylenes or the like. Using volatile organic compounds and manually rotating the printing press and cleaning off the blanket section-by-section, by the time the bottom of the blanket is cleaned, the volatile cleaner will have evaporated to dryness from the previously cleaned sections. In view of environmental concerns and ever-tightening EPA restrictions concerning the use of volatile organic compounds, there is a desire to find compositions which can be used to remove ink from the rubber blanket and other members of a printing press without undue amounts of machine downtime. U.S. Pat. No. 5,104,567 discloses a conventional cleaning composition which comprises 90-99% soy oil and 1-10% emulsifier. While such compositions are devoid of volatile organic compounds, they are significantly less effective than such volatile compounds for ink removal. With respect to such conventional cleaning compositions comprising soybean oil and emulsifier, it is common to have to clean the rubber blanket with more than one application of cleaner. Typically, this involves vigorously scrubbing the rubber blanket with cleaner; rinsing it with water, and then re-applying the cleaner one or more times to get the blanket sufficiently clean. Additionally, the pressman must completely remove the cleaner from the rubber blanket (i.e., wipe the blanket dry) prior to resuming the printing operation. If the conventional cleaning compositions comprising soy oil and emulsifiers are not completely removed, they will contaminate, break-down and reduce the tack of the ink on the ink-bearing components of the press including the image plate and blanket. If that occurs, the cleaning procedure will have to be repeated, and the components dried, before printing can resume.
Lithographic printing presses with automatic blanket washers are also known. Automatic blanket washers have a sprayer means for spraying a cleaner composition onto the rubber blanket and a removing means for removing the cleaner/ink mixture. Typically, an automatic blanket washer sprays a metered amount of cleaner onto the blanket while the press is at idle speed with the blanket disengaged from the image plate. In one well known apparatus the ink/cleaner removing means comprises an inflatable bladder having affixed thereto a woven cloth material (e.g., woven polyester). The bladder is inflated to bring the cloth material into contact with the rotating blanket, whereby the ink/cleaner mixture is rubbed off. Conventional cleaner compositions devoid of volatile organic compounds are not suitable for use in automatic blanket washers. Prior to the present invention, volatile organic compounds were required so evaporation would dry the blanket prior to the resumption of printing.
Thus, it would be very desirable to provide ink cleaning compositions which are devoid of, or have reduced amounts of, volatile organic compounds, and which are effective for removing ink from the parts of a printing press. It would also be very desirable to provide cleaning compositions which have low or no volatile organic compounds and are compatible with ink compositions so that the cleaning compositions do not have to be dried from the parts of the press, especially the rubber blanket, before printing is resumed.